The statements in this section merely provide background information related to the present disclosure and may not constitute prior art.
High-voltage systems such as high-voltage on-board electrical systems are used, for example, in electric or hybrid vehicles. A high-voltage on-board electrical system includes a high-voltage power storage device such as a high-voltage battery that makes a high voltage available for supplying a load coupled to the high-voltage power storage device.
When mechanical switches in high-voltage on-board systems are actuated, the momentary switching state is frequently not known. However, especially in failsafe critical applications such as coupling the high-voltage power storage device to the load, it is important to know whether the mechanical switch is open or closed or whether there is a malfunction.
One known solution provides that the voltage dropping at the mechanical switch be monitored and compared to a defined threshold value. With this comparison it is possible to recognize whether the mechanical switch is open or closed. Evaluating the characteristics of the voltage dropping at the mechanical switch is also known.
One of the issues involved in determining the switching state of these mechanical switches resides in ascertaining and identifying suitable threshold values that enable reliable recognition of the switching state under as many (variable) boundary conditions and/or system states of the high-voltage on-board electrical system as possible. Here the voltage drops to be evaluated at the mechanical switches depend heavily on the capacitances and resistances present in the system. Voltages may differ depending on the field of application, for which reason it is sometimes difficult to evaluate the voltage drops by comparison with the defined threshold value or in evaluating the voltage characteristics. Thus, a reliable evaluation is not always possible.
An open mechanical switch may be recognized as being closed if the voltage drop used for comparative purposes lies below the defined threshold value. This can be caused, for example, by altered boundary conditions and/or system states. The mechanical switch is then erroneously recognized as being closed and/or defective, when in fact it has been properly opened and is in working order. False recognition of the switching state of the mechanical switch can lead to malfunctions in the high-voltage on-board electrical system.
DE 10 2014 117 417 A1 discloses a battery management system for a high-voltage battery, the battery management system comprising a switching device with controllable switching elements for establishing and disconnecting the electrical connection between the poles of the high-voltage battery and the connection points for a consumer network; a device for insulation monitoring, wherein the poles and the connection points are each switched via a voltage divider to a reference potential for insulation measurement, characterized in that the battery management system further comprises a device for checking the switching status of the controllable switching elements by measuring devices to determine the electrical voltage, wherein the measuring devices are arranged so that they measure the voltage between output of the respective voltage divider and the reference potential, and wherein the device for checking the switching status of the controllable switching elements has a device for comparing the measured voltage values of those two measuring devices with a controllable switching element switched between each of their assigned voltage dividers.
DE 10 2006 050 529 A1 describes a switching arrangement to monitor the insulation and contactors of the power supply of an electric drive, comprising a battery to supply the power to the electric drive; power electronics fed by the battery to actuate an electric motor of the electric drive; one or more contactors for the all-pole electrical disconnection of the battery from the power electronics; a voltage source connected to a reference potential to generate a measuring voltage for monitoring the insulation and the contactors; two voltage measuring devices to measure a voltage excursion produced by the measuring voltage in relation to the reference potential, wherein the voltage source and a first voltage measuring device are electrically connected to a feed point for supplying the measuring voltage and a second voltage measuring device is electrically connected to a measuring point for measuring the voltage excursion, and the feed point and measuring point are arranged such that the at least one contactor is connected between them.
There is a demand for a simpler and more reliable way to recognize the switching state of the mechanical switch through which a high-voltage power storage device is capable of being coupled especially to a load.